Control for a target common bus voltage

ABSTRACT

In some examples, a system includes a bus and a first power converter connected to the bus. The system also includes a second power converter connected to the bus, the second power converter having a topology different from the topology of the first power converter. The system further includes a power source and an energy storage device connected to the bus via the first and second power converters, respectively. In addition, the system includes a source controller configured to control the first power converter and a storage controller configured to control the second power converter. The system also includes a system controller configured to determine a first set point for the first power converter, transmit an indication of the first set point to the source controller, determine a second set point for the second power converter, and transmit an indication of the second set point to the storage controller.

TECHNICAL FIELD

This disclosure relates to electrical power systems.

BACKGROUND

A bus bar in an electrical power system can deliver power from a powersource to a load that is remote form the power source. A first powerconverter can supply power generated by the power source to the bus bar,and a second power converter can deliver power from the bus bar to theload. An energy storage device can act as a load or as a power source bysupplying or consuming power, depending on the circumstances. Oneexample is an electrical power system onboard an aircraft that includesa generator configured to convert mechanical energy of an engine intoelectrical energy for distribution on a bus bar to a remote propulsor.The aircraft can include a motor that drives the propulsor based onpower received from the bus bar. In this way, the engine can drive theremote propulsor and provide power to other loads onboard the aircraft.

SUMMARY

This disclosure describes techniques for controlling energy resourcesthat are connected to a bus in an electrical power system. The energyresources may include a power source, an energy storage device, and aload. A system controller may be configured to send commands to a firstprimary controller that is configured to control the power source, to asecond primary controller that is configured to control the energystorage device, and/or to a third primary controller that is configuredto control the load.

The techniques of this disclosure may allow for management of all of theenergy resources connected to the bus. Each primary controller may beconfigured to implement a droop power curve based on locally sensedparameters, which may allow for the primary controllers to quicklyrespond to disturbances on the bus. The primary controllers may be ableto effectively maintain the voltage magnitude on the bus with relativelysmall transients regardless of the operating modes of the power sources,energy storage devices, and loads.

In some examples, a system includes a bus and a first power converterconnected to the bus. The system also includes a second power converterconnected to the bus, the second power converter having a topologydifferent from the topology of the first power converter. The systemfurther includes a power source and an energy storage device connectedto the bus via the first and second power converters, respectively. Inaddition, the system includes a source controller configured to controlthe first power converter and a storage controller configured to controlthe second power converter. The system also includes a system controllerconfigured to determine a first set point for the first power converter,transmit an indication of the first set point to the source controller,determine a second set point for the second power converter, andtransmit an indication of the second set point to the storagecontroller.

In some examples, a method includes determining, by a system controller,a first set point for a first power converter connected to a bus,wherein the first power converter has a first topology. The method alsoincludes transmitting, by the system controller, an indication of thefirst set point to a source controller, wherein the source controller isconfigured to control the first power converter. The method furtherincludes determining, by the system controller, a second set point for asecond power converter connected to the bus, wherein the second powerconverter has a second topology, and the first topology being differentfrom the second topology. The method includes transmitting, by thesystem controller, an indication of the second set point to a storagecontroller, wherein the storage controller is configured to control thesecond power converter.

In some examples, a device includes a computer-readable medium havingexecutable instructions stored thereon, configured to be executable byprocessing circuitry for causing the processing circuitry to determine afirst set point for a first power converter connected to a bus, whereinthe first power converter has a first topology. The instructions areconfigured to be executable by the processing circuitry for also causingthe processing circuitry to transmit an indication of the first setpoint to a source controller, wherein the source controller isconfigured to control the first power converter. The instructions areconfigured to be executable by the processing circuitry for furthercausing the processing circuitry to determine a second set point for asecond power converter connected to the bus, wherein the second powerconverter has a second topology, and the first topology being differentfrom the second topology. The instructions are configured to beexecutable by the processing circuitry for causing the processingcircuitry to transmit an indication of the second set point to a storagecontroller, wherein the storage controller is configured to control thesecond power converter.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual block diagram illustrating a system includingthree different types of energy resources connected to a bus, inaccordance with one or more techniques of this disclosure.

FIG. 2 is a conceptual block diagram illustrating a controller for anenergy resource, in accordance with one or more techniques of thisdisclosure.

FIG. 3 is a conceptual block diagram illustrating a system controller,in accordance with one or more techniques of this disclosure.

FIG. 4 is a timing diagram illustrating the charging and discharging ofan energy storage device, in accordance with one or more techniques ofthis disclosure.

FIG. 5 is a diagram illustrating a voltage deadband for an energystorage device, in accordance with one or more techniques of thisdisclosure.

FIG. 6 is a conceptual block diagram illustrating voltage versus currentdroop implementation method, in accordance with one or more techniquesof this disclosure.

FIG. 7 is a conceptual block diagram illustrating high- and low-voltageenergy storage devices, in accordance with one or more techniques ofthis disclosure.

FIG. 8A is a conceptual block diagram illustrating a system controllerin the context of a storage fault, in accordance with one or moretechniques of this disclosure.

FIG. 8B is a conceptual block diagram illustrating a system controllerfor generating a load set point, in accordance with one or moretechniques of this disclosure.

FIG. 9 is a conceptual block diagram illustrating a charging circuit fortwo energy storage devices, in accordance with one or more techniques ofthis disclosure.

FIGS. 10A and 10B are plots illustrating a change in a set point, inaccordance with one or more techniques of this disclosure.

FIG. 11 is a flowchart illustrating an example process for operating asystem controller, in accordance with one or more techniques of thisdisclosure.

FIG. 12 is a flowchart illustrating an example process for operating astorage controller, in accordance with one or more techniques of thisdisclosure.

FIG. 13 is a flowchart illustrating an example process for operating aload controller, in accordance with one or more techniques of thisdisclosure.

FIG. 14 is a flowchart illustrating an example process for operating asystem controller based on user input, in accordance with one or moretechniques of this disclosure.

DETAILED DESCRIPTION

This disclosure describes techniques for controlling distributed energyresources (e.g., sources, loads, and storage devices) that are connectedto an electrical bus for transferring power from one or more sources toone or more loads. In addition, one or more energy storage devices maybe connected to the bus, where each energy storage device can act as asource or a load. Each energy resource in the system may be connected tothe bus via a power converter, and the system may include a plurality ofindividual controllers, also referred to as primary controllers. Eachindividual controller is configured to control a respective powerconverter in a droop control mode, where the individual controller cancontrol a respective power converter based on one or more parameters(e.g., a sensed signal and/or a set point) without direct control fromthe a centralized controller. A controller operating in droop controlmode may operate on its own without communicating with any othercontroller, except for receiving commands from a system controller toset threshold levels.

In some examples, each of the energy resources are connected to the busvia a respective power converter, where each power converter has aparticular topology. For example, a power source may be connected to thebus via a rectifier that converts alternating current (AC) electricityproduced by the power source to direct current (DC) electricity fordelivery to the bus. A load may be connected to the bus via an inverterthat converts DC from the bus to AC for use by the load (e.g., to drivethe load). An energy storage device may be connected to the bus via aDC/DC converter that converts the DC voltage across the terminals of thestorage device to the DC voltage on the bus. A system controller may beconfigured to send a set point command to each of the converters, whereconverters may have a different topology (e.g., rectifier(s),inverter(s), and/or DC/DC converters). Each of the controllers and powerconverters are integrated into the system and operate together despitethe differing topologies and types.

The distributed controllers may be capable of coordinated modetransitions, such as a transition to a high-propulsion mode where one ormore of the propulsors consume more power than during normal operation.During a high-propulsion mode, the power sources generate power and theenergy storage devices operate in discharge mode to deliver electricityto the loads. Another example transition is to a charging mode where theenergy storage devices receive power generated by the power sources.These transitions can be performed by the primary controllersimplementing droop curves, in some cases without coordination betweenthe primary controllers and/or without direction from a systemcontroller. The energy resource power flow transitions are maintained bythe commands sent by the system controller to each of the primarycontrollers. The transitions between operating modes may be relativelyeasy because of the autonomy of the primary controllers.

The primary controllers may be designed to react quickly to modetransitions because of the autonomy of the primary controllers. Thesystem may be able to smoothly transition from one mode to another modewithout changing any of the control loops in any of the controllers orenergy resources. Quick action by the local, autonomous controllers mayresult in a well-maintained bus voltage that is kept within certainlimits, which may be especially useful for aerospace applications inwhich stable propulsion without substantial deviations is desirable.Thus, because of this stable, well-maintained bus voltage, the systemmay be designed with fewer and/or smaller capacitors, which can lowerthe size, weight, cost, and complexity of the system, as compared to anexisting system.

Each energy storage device may be connected to the bus via a respectivepower converter that is controlled by a storage controller. The storagecontroller may be configured to operate the power converter with avoltage deadband, which may reduce the fatigue experienced by the energystorage device that can result from excessive charge and dischargecycles. The storage controller may be configured to set the thresholdsfor the voltage deadband based on commands received from a systemcontroller.

Each load may be connected to the bus via a respective power converterand a respective motor that are controlled by a load controller. Theload controller may be configured to operate the power converter andload with a modified voltage deadband, whereby the controller may reducethe power drawn from the bus by the load when the bus voltage dropsbelow a threshold level. The modified deadband may allow for reductionof the power drawn by the load when the voltage magnitude on bus 120deviates downward.

FIG. 1 is a conceptual block diagram illustrating a system 100 includingthree different types of energy resources 140, 150, and 160 connected toa bus 120, in accordance with one or more techniques of this disclosure.Although FIG. 1 depicts three energy resources (e.g., a single powersource 140, a single energy storage device 150, and a single load 160),system 100 may include one or more power sources 140, one or more energystorage devices 150, and/or one or more loads 160. Power source 140 maybe referred to as energy resource 140, energy storage device 150 may bereferred to as energy resource 150, and load 160 may be referred to asenergy resource 160. For example, power source 140 may represent two ormore generators, energy storage device 150 may represent two or morebatteries, load 160 may represent two or more propulsors. In addition,system 100 may also include different types of power sources, differenttypes of energy storage devices, and/or different types of loads 160. Inother words, there may be any number and any type of sources, storagedevices, and loads in system 100. Two or more components can share asingle power converter, or each component may have a dedicated powerconverter.

In some examples, system 100 is a hybrid electric propulsion systemincluding multiple generation systems, energy storage devices, and loadsin an aerospace application. The control coordination among all of theprimary controllers 144, 154, and 164 in various operating modes is animportant concern for a successful and effective hybrid electricpropulsion solution in aerospace applications. To accomplish thiscontrol coordination and maintain a desired bus voltage, systemcontroller 110 may be configured to establish and transmit set points tothe primary controllers 144, 154, and 164, as described in furtherdetail below.

Bus 120 may include a DC bus and/or an AC bus, such as a high-voltage DCbus. In some examples, bus 120 includes a differential bus with ahigh-side rail and a low-side rail. Additionally or alternatively, bus120 may include a ground rail, which may be connected to a chassis,frame, or housing of system 100. Bus 120 may carry a voltage potentialof one hundred volts, 270 volts, 540 volts, 1080 volts, and/or any othervoltage level. The voltage magnitude on bus 120 may increase as powersource 140 generates more power, and the voltage magnitude on bus 120may decrease as load 160 consumes more power.

Power source 140 may include a gas turbine engine driving, for example,two generators. The two generators may have a common central shaft withtwo different electromagnetic generators within the housing that arepositioned around and coaxial with the shaft. In some examples, powersource 140 includes two generators with side-by-side stators that may beenclosed in the same housing. Each generator may be connected to commonbus 120 via an individual AC/DC converter. In addition, energy storagedevice 150 is connected to the same common DC bus 120 via DC/DCconverter. Power source 140 may include a wound field machine, a Halbacharray generator with permanent magnets on a rotor that is driven by anengine shaft or a propulsor shaft, or any other type of generator.

Energy storage device 150 is connected to bus 120 via power converter152. Power converter 152 may include a DC/DC converter for boosting thevoltage across the terminals of energy storage device 150 to the voltagemagnitude on bus 120 and/or stepping down the voltage magnitude on bus120 to the voltage across the terminals of energy storage device 150.For example, the desired voltage magnitude on bus 120 may be 1,080volts, and the voltage across the terminals of energy storage device 150may be approximately eight or nine hundred volts.

Load 160 may include any component that receives power from bus 120.Common bus 120 delivers power to load 160, and load 160 may representtwo or more motors, each configured to drive a propulsor. Each motor mayinclude a gearbox to interface with the propulsor. Each motor may bedriven by AC electricity received from power converter 162, or eachmotor may be driven by AC electricity received from a separate,dedicated power converter. Load 160 may be configured to operate atmultiple different power levels, where load controller 164 can controlpower converter 162 to achieve a desired power level for load 160.

Each of power converters 142, 152, and 162 are controlled by arespective primary controller. Additional example details of powerconverters in an electrical power system are described in commonlyassigned U.S. Pat. No. 10,693,367, entitled “Pre-Charging Circuit forPower Converters,” issued on Jun. 23, 2020; U.S. patent application Ser.No. 16/951,269, entitled “Fault Detection for a Solid State PowerConverter,” filed on Nov. 18, 2020; and U.S. patent application Ser. No.17/100,225, entitled “Fault Detection for a Solid State PowerConverter,” filed on Nov. 20, 2020, the entire contents of which areincorporated herein by reference.

Each of controllers 144, 154, and 164 may be configured to receive asensed signal indicating a voltage magnitude on bus 120. For example,each controller may have a nearby, dedicated respective sensor forsensing the bus voltage. In other words, system 100 may include a firstvoltage sensor on bus 120 near power converter 142, where sourcecontroller 144 receives a signal from the first voltage sensor. System100 may also include a second voltage sensor on bus 120 near powerconverter 152 and a third voltage sensor on bus 120 near power converter162, where storage controller 154 receives a signal from the secondvoltage sensor and load controller 164 receives a signal from the thirdvoltage sensor. The voltage magnitude may be relatively uniform acrossbus 120, such that each of the voltage sensor may sense approximatelythe same voltage level. The voltage sensors may include a magneticsensor, a current mirror, a shunt resistor, and/or any other type ofvoltage sensor.

In addition, each of controllers 144, 154, and 164 may be configured tosense the current and voltage of/across the respective one of energyresources 140, 150, and 160. For example, source controller 144 may beconfigured to receive signals indicating the voltage across theterminals of power source 140 and the current on each line of powersource 140 (e.g., multiphase lines). Each of controllers 144, 154, and164 may be configured to determine the magnitude of power received orproduced by the respective one of energy resources 140, 150, and 160based on the sensed voltage and current. Each of controllers 144, 154,and 164 may be configured to sense local parameters, control therespective power converter based on the sensed parameters, and sharepower on bus 120.

In some examples, controllers 144, 154, and 164 may not have any mutualcommunication among the controllers. However, each of controllers 144,154, and 164 may be configured to individually receive commands fromsystem controller 110 via a slow communication line, where systemcontroller 110 may include a supervisory hybrid system controller (HSC).System controller 110 may be configured to initiate various ranges ofcommands to all the downstream primary controllers (e.g., controllers144, 154, and 164) for various modes of operation. Controllers 144, 154,and 164 are configured to decode the communications from systemcontroller 110 and execute the operating mode commanded by systemcontroller 110.

Each of controllers 110, 144, 154, and 164 may include processingcircuitry, which can include any suitable arrangement of hardware,software, instructions, firmware, or any combination thereof, to performthe techniques attributed to controllers 144, 154, and 164 herein.Examples of processing circuitry include any one or more microprocessors(e.g., a central processing unit—CPU, a graphics processing unit—GPU,and the like), digital signal processors (DSPs), application specificintegrated circuits (ASICs), full authority digital engine control(FADEC) units, engine control units (ECUs), field programmable gatearrays (FPGAs), or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. When theprocessing circuitry includes software or firmware, the processingcircuitry further includes any hardware for storing and executing thesoftware or firmware, such as one or more processors or processingunits.

In general, a processing unit may include one or more microprocessors,DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. Although notshown in FIG. 1 , each of controllers 110, 144, 154, and 164 may includea memory configured to store data. The memory may include any volatileor non-volatile media, such as a random access memory (RAM), read onlymemory (ROM), non-volatile RAM (NVRAM), electrically erasableprogrammable ROM (EEPROM), flash memory, and the like. In some examples,the memory may be external to controllers 110, 144, 154, and 164 (e.g.,may be external to a package in which one of controllers 110, 144, 154,and 164 is housed). The processing circuitry of controllers 110, 144,154, and 164 may be configured to determine whether a sensed signalindicating the voltage magnitude on bus 120 is greater than or less thana threshold level. For example, the processing circuitry may includecircuitry (e.g., digital or analog) and/or instructions for performingthresholding operations. Where this disclosure describes a controllerdetermining whether a sensed signal is greater than or less than athreshold level, the controller may also determine whether the sensedsignal is greater than or equal to the threshold level or determinewhether the sensed signal is less than or equal to the threshold levelin some instances.

It may be desirable to maintain the voltage magnitude on bus 120 withina target range. For example, the target range may be a range of DCvoltage magnitudes or one or more ranges of frequencies, phases, andamplitudes. Maintaining the target voltage on bus 120 may allow for load160 to operate in a desirable manner. For example, load 160 may be ableto produce a desired amount of thrust when the voltage magnitude on bus120 is within the target range. When the voltage magnitude on bus 120deviates substantially downward, load 160 may no longer be able tofunction as desired.

One design technique for maintaining a target voltage on a bus is for asystem controller to directly command each primary controller toincrease to decrease power generation or power draw. This requiresextensive communication between the system controller and all of theprimary controllers that receive commands from the system controller.

Another design technique is to have system-level controller(s) that onlycommunicate with primary controllers for like-type power converters. Forexample, an existing system can use droop control may include like-typepower converters, where each droop controller controls the same type ofpower converter connected to the same type of energy resource. Forexample, an array of generators in an existing system may each beconnected to a bus via a rectifier, where each droop controller controlsone of the rectifiers. As used herein, the term “like-type” may refer toa set of rectifiers, a set of DC/DC converters, or a set of inverters.An inverter may be a non-like-type converter with respect to arectifier.

In accordance with the techniques of this disclosure, system controller110 is configured to send commands to two or more of controllers 144,154, and 164, where these droop controllers control non-like-type powerconverters, and where at least two of the power converters have adiffering topologies. A first topology may be a rectifier, a secondtopology may be a DC/DC converter (e.g., a boost or buck converter), anda third topology may be an inverter. In some examples, a rectifier maybe arranged using the same topology as an inverter, but operated in areverse direction. For example, system controller 110 can send a commandto source controller 144, which may control a rectifier (e.g., powerconverter 142) connected between power source 140 and bus 120. Systemcontroller 110 can also send a command to storage controller 154, whichmay control a DC/DC converter (e.g., power converter 152) connectedbetween energy storage device 150 and bus 120. Thus, power converters142 and 152 may be non-like-type power converters that are integratedunder the system droop control scheme. In addition, system controller110 may be configured to also send a command to load controller 164,which may control an inverter (e.g., power converter 162) connectedbetween load 160 and bus 120.

Responsive to receiving a command from system controller 110, each ofcontrollers 144, 154, and 164 may be configured to set a threshold levelfor the voltage magnitude on bus 120. Each of controllers 144, 154, and164 may be configured to compare the sensed voltage magnitude on bus 120to the threshold level to determine how to control the respective one ofpower converters 142, 152, and 162. For example, responsive todetermining that the voltage magnitude on bus 120 is less than thethreshold level, each of controllers 144, 154, and 164 may be configuredto increase the power delivered to bus 120 and/or to decrease the powerdrawn from bus 120. Responsive to determining that the voltage magnitudeon bus 120 is greater than the threshold level, each of controllers 144,154, and 164 may be configured to decrease the power delivered to bus120 and/or to increase the power drawn from bus 120.

During each mode of operation, the algorithms implemented by controllers144, 154, and/or 164 may not change. But controllers 144, 154, and 164may be configured to seamlessly carry out each mode in order to maintaina stable common DC bus voltage without any visible or damaging transientreflections during control mode switchovers. According to controlcertification requirements for aerospace standard demands, controllers144, 154, and 164 may have almost no change in control loops. Thus, acoordination control strategy named “Universal Autonomous Control” (UAC)has a single control algorithm framework for all of controllers 144,154, and 164 so that commands from system controller 110 can beautomatically decoded by controllers 144, 154, and 164. In someexamples, each of controllers 144, 154, and 164 can operate without anymutual communication, such as communication between controllers 144 and154 or between controllers 144 and 164. Controllers 144, 154, and 164may be configured to execute the specific mode indicated in the commandfrom system controller 110 without having to coordinate among thecontrollers 144, 154, and 164.

Additionally, all different types of distributed energy resources can beconnected to bus 120 using a unified primary and secondary controlstrategy. As a primary control strategy, system controller 110establishes and transmits set points to controllers 142, 152, and 162.Thus, in the example of an aerospace application, power source 140generates a sufficient amount of power to maintain a stable bus voltageso that load 160 can generate the desired amount of propulsion.

From a secondary control point of view, all of the energy resources areidentified as similar items, even though the actual energy resourcesdiffer by type. In addition, the switching frequencies of powerconverters 142, 152, and 162 that connect energy resources 140, 150, and160 to bus 120 may be widely different. For example, power converter 142may include a rectifier, and source controller 144 may be configured tocause power converter 142 to switch at thirty-five kilohertz. Powerconverter 152 may include a DC/DC converter, and storage controller 154may be configured to cause power converter 152 to switch at sixty-fivekilohertz. Each of controllers 144, 154, and 164 may be configured tointerface with a respective one of power converters 142, 152, and 162 byactivating and deactivating the switches of the respective powerconverter. In other words, each of controllers 144, 154, and 164 cancause the respective power converter to deliver, transfer, and/or draw aparticular magnitude of power to or from bus 120.

System 100 may be configured to operate in various modes, where eachmode is designed for a specific situation. In the context of aviation,the modes may be designed by in-flight, take-off, landing, cruise,and/or ground charging of energy storage device 150. System 100 may beconfigured with various operating conditions where power source 140 andenergy storage device 150 are able to balance the load demand. Using UACprinciples, controllers 144, 154, and 164 may be configured to establishset points and/or implement operating modes based on commands receivedfrom system controller 110. Controllers 144, 154, and 164 may beconfigured to also control power converters 142, 152, and 162 based onthe set points and further based on locally sensed parameters. Thiscontrol strategy may allow for quick responses to fluctuations in thevoltage magnitude on bus 120 because of the seamless and autonomousoperation of the primary controllers.

FIG. 2 is a conceptual block diagram illustrating a controller 234 foran energy resource 230, in accordance with one or more techniques ofthis disclosure. Controller 234 may represent one example of controller144, 154, and/or 164 shown in FIG. 1 . Controller 234 may be configuredto implement an individual droop scheme in the primary control block asshown in FIG. 2 . Controller 234 may control an AC/DC converter for aturbo generator or a DC/DC converter for an energy storage device.Controller 234 may be configured to implement an individual primarycontrol strategy that includes a voltage-to-power droop section 240,outer voltage control loop 250, and inner current control loop 260.

In the example shown in FIG. 2 , section 240 receives a first valueindicating the sensed power generated or drawn by energy resource 230and multiplies the first value by a droop gain for energy resource 230.Section 240 also receives a second value from the system controller,where the second value indicates the voltage set point for energyresource 230 and subtracts the product of the first value from thesecond value.

Voltage loop 250 receives the output of section 240 and subtracts athird value indicating a sensed voltage magnitude on bus 220 to generatea quadrature voltage reference. Controller 234 may be configured todetermine the voltage magnitude based on a sensed signal received from avoltage sensor on bus 220 near power converter 232. Voltage loop 250includes a proportional-integral controller configured to generate atarget quadrature current based on the quadrature voltage reference, andcurrent loop 260 subtracts an actual quadrature current from the targetquadrature current. Voltage loop 250 also generates a target directcurrent based on the direct current, and current loop 260 subtracts anactual direct current from the target direct current. Controller 234processes the outputs of current loop 260 and waveform 270 to generatecontrol signals for power converter 232, which may include a pulse-widthmodulation (PWM) signal with a switching frequency and a duty cycle.

A storage controller may include similar modules to controller 234,except that the storage controller may not include the direct andquadrature currents. Instead, the storage controller may include avoltage loop that generates a target current and a current loop thatsubtracts an actual current from the target current. The storagecontroller then processes the outputs of the current loop and a waveformto generate control signals for a DC/DC converter.

Inner current loop 260 may include a proportional integrator controller.The gains of inner current loop 260 can be set in such a way that thebandwidth of current loop 260 is less than the respective switchingfrequency, less than one-half of the switching frequency, less thanone-fifth of the switching frequency, and/or less than one-tenth of theswitching frequency. Control loops 250 and 260 may be fast enough sothat controller 234 is able to continuously react to disturbances in thevoltage magnitude on bus 220. The switching frequency may depend on thetype of energy resource 230 and power converter 232, the switchingsignal (e.g., control signal) may be a PWM signal generated by comparingthe output of current loop 260 to waveform 270. Controller 234 can usethe switching signal(s) to activate and deactivate the switches of powerconverter 232. In some examples, the system may also include a gatedriver circuit for amplifying the power of the control signals beforedelivering the amplified control signals to the switches of powerconverter 232.

To make the control scheme work properly, the gains of voltage loop 250can be set so that the bandwidth of current loop 260 is of the sameorder for an AC/DC converter connected to a power source and a DC/DCconverter connected to an energy storage device, for example, one-tenthof the maximum electrical frequency of the AC power source. In someexamples, the bandwidth of current loop 260 is less than one-fifth ofthe operating frequency of an AC power source. The individual AC/DC andDC/DC voltage versus the gain of the power droop curve can be set basedon the maximum power and power transfer capability of converter 232. Thesystem controller may be configured to initiate a command to eachconverter via a slow communication bus only without any inter-convertercommunication.

In some examples, a control scheme for an electrical power system mayinclude control of a DC/DC power converter for an energy storage devicethat is fully synchronized with control of an AC/DC converter for apower source. Operation modes for the electrical power system includecharging of an energy storage device, discharging of the energy storagedevice, buck mode when a low-voltage energy storage device is faulty butan auxiliary load is still receiving power from the bus simultaneously,and a mode with no change in primary control in any of the converters.In charging, discharging, and buck modes, of the converters, energystorage devices, and controllers in the electrical power system may beoperating in a universal autonomous control mode. The voltage magnitudeon the bus can be maintained to a rated value in steady-state (e.g.1,080 volts) in all modes. Each of the primary controllers may beconfigured to automatically decode the commands received from the systemcontroller possibly without any direct communication among the primarycontrollers.

FIG. 3 is a conceptual block diagram illustrating a system controller310, in accordance with one or more techniques of this disclosure.System controller 310 may represent one example of system controller 110shown in FIG. 1 . System controller 310 includes set point module 312for determining set points for a source controller and for a storagecontroller based on sensed parameters and based on user commands. Thesensed parameters may include the voltage magnitude on the bus, thepower generated by a source, the power drawn by a load, and the powerdischarged or drawn by an energy storage device. The user commands mayinclude one or more power commands for an energy storage device and oneor more loads and a voltage command for the voltage magnitude on thebus. Set point module 312 may also determine the storage and sourcedroop gains based on the sensed parameters.

Equations (1)-(3) show the relationship between the voltage referencefor an energy storage device (V_(Bref)) and the voltage references fortwo power sources (V_(G1ref) and V_(G2ref)) and the droop gains (D_(B)and D_(G)). Equations (4) and (5) show the output power of the DC/DCconverter connected to the energy storage device (P_(B)) and the outputpower of the AC/DC converter connected to the power sources (P_(G1) andP_(G2)) based on the total load power (P_(L)) and the number ofgenerators (N_(G)) in operation. Equations (6) and (7) show the voltagemagnitude of the bus due to activated power sources and energy storagedevice operation.

$\begin{matrix}{V_{Bref} = {V_{B}^{*} - {D_{B}P_{B}}}} & (1)\end{matrix}$ $\begin{matrix}{V_{G1{ref}} = {V_{G}^{*} - {D_{G}P_{G1}}}} & (2)\end{matrix}$ $\begin{matrix}{V_{G2{ref}} = {V_{G}^{*} - {D_{G}P_{G2}}}} & (3)\end{matrix}$ $\begin{matrix}{P_{B} = {\frac{1}{D_{B}}\left\lbrack {V_{B}^{*} - \frac{\left( {\frac{V_{B}^{*}}{D_{B}} + \frac{N_{G} \times V_{G}^{*}}{D_{G}}} \right) - P_{L}}{\left( {\frac{1}{D_{B}} + \frac{N_{G}}{D_{G}}} \right)}} \right\rbrack}} & (4)\end{matrix}$ $\begin{matrix}{P_{G1},{P_{G2} = {P_{G} = {\frac{1}{D_{G}}\left\lbrack {V_{G}^{*} - \frac{\left( {\frac{V_{B}^{*}}{D_{B}} + \frac{N_{G} \times V_{G}^{*}}{D_{G}}} \right) - P_{L}}{\left( {\frac{1}{D_{B}} + \frac{N_{G}}{D_{G}}} \right)}} \right\rbrack}}}} & (5)\end{matrix}$ $\begin{matrix}{V_{HVDC} = {V_{B}^{*} - \left( {D_{B} \times P_{B}} \right)}} & (6)\end{matrix}$ $\begin{matrix}{V_{HVDC} = {{V_{B}^{*} - {\frac{D_{B}}{D_{B}}\left\lbrack {V_{B}^{*} - \frac{\left( {\frac{V_{B}^{*}}{D_{B}} + \frac{N_{G} \times V_{G}^{*}}{D_{G}}} \right) - P_{L}}{\left( {\frac{1}{D_{B}} + \frac{N_{G}}{D_{G}}} \right)}} \right\rbrack}} = \frac{\left( {\frac{V_{B}^{*}}{D_{B}} + \frac{N_{G} \times V_{G}^{*}}{D_{G}}} \right) - P_{L}}{\left( {\frac{1}{D_{B}} + \frac{N_{G}}{D_{G}}} \right)}}} & (7)\end{matrix}$

The system controller may be configured to iteratively determine thevoltage set points using Equations (1)-(3) until the sensed power flowthrough each power converter is close enough to the power set points(e.g., within an acceptable range). The no-load droop settings ofdifferent AC/DC and DC/DC converters can be adjusted and initiated bythe system controller to make sure the appropriate power flows from thedistributed energy resources. In addition, the HVDC bus voltagemagnitude can be set to the desired value. Equations (8) and (9) showtwo conditions: battery discharge or charge, and neither charge nordischarge.

$\begin{matrix}{{V_{G}^{*} - V_{B}^{*}} = {{P_{L}\frac{D_{G}}{N_{G}}} - {P_{B}\frac{D_{G} + {N_{G}D_{B}}}{N_{G}}}}} & (8)\end{matrix}$ $\begin{matrix}{V_{HVDC} = {V_{B}^{*} - {D_{B}P_{B}}}} & (9)\end{matrix}$

FIG. 4 is a timing diagram illustrating the charging and discharging ofan energy storage device, in accordance with one or more techniques ofthis disclosure. Power source 140 and energy storage device 150 shown inFIG. 1 may be configured to operate in the power generation, charging,and discharging modes depicted in FIG. 4 . Using the system frameworkdescribed herein, the mode transitions depicted in FIG. 4 can occurwithout coordination by a central controller. Instead, the systemcontroller can issue a command to one or more of the primarycontrollers, and the remaining primary controllers will react to changesin the voltage magnitude on the bus.

In phase 410, the energy storage device discharges to regulate thevoltage magnitude on the bus, and the power sources start up at lowload. In phase 412, the energy storage device and the power sourcesproduce approximately equal amounts of power. In phase 414, the powersources produce all of the power for the system, while the energystorage device is not charging or discharging. In phase 416, the powersources ramp up the power generation, while the energy storage device isnot charging or discharging.

In phase 418, the storage controller causes the energy storage device tocharge using power received from the bus. In addition, in phase 418, thepower sources further increase power generation to provide power for theenergy storage device and loads within the system. In phase 420, theenergy storage device returns to not charging or discharging, and thepower sources produces all of the power consumed by the load. In phase422, the energy storage device begins discharging to provide power,while the power sources continue producing power but at a lower ratethan phases 418 and 420.

The mode transitions shown in FIG. 4 can be made without coordination bya central controller. For example, to transition from phase 410 to phase412, the system controller can send a command to the sourcecontroller(s) to produce more power, which may increase the voltagemagnitude on the bus. The storage controller senses the increasedvoltage magnitude on the bus and reduces the discharge rate of theenergy storage device. A similar command from the system controller maycause the transition from phase 412 to phase 414. As another example,the system controller may command the storage controller to enter acharging mode in phase 418. The source controller(s) may be configuredto cause the power sources to produce more power in phase 418 inresponse to sensing the voltage magnitude on the bus has dropped afterthe energy storage device begins charging.

In contrast, a centralized system could experience large spikes,troughs, and hard transients in the voltage magnitude on the bus. Forexample, a central controller would command an energy storage device tobegin discharging and would also command a power source to produce lesspower. The commands would likely be implemented by the storagecontroller and source controller at different times, and there would bea considerable lag in the implementation by one of the controllers. Thelag in implementation would result in too much power being delivered toor drawn from the bus. For even a small amount of time, this additionalpower would cause a substantial change in voltage that pushes thevoltage magnitude on the bus outside of the acceptable range.

The capacitors in a system of this disclosure may be few and/or small,meaning that a small change in energy may cause a relatively largechange in the voltage magnitude on the bus. Without large capacitors onthe bus, the bus voltage may move quickly. It may be desirable to notadd capacitors to the system because of the size, weight, cost, andmanufacturing time and complexity involved with adding capacitors to asystem. A decentralized control scheme may allow for quickly respondingto undesirable changes in bus voltage.

Additional example details of determining a desired power set point foran energy storage device are described in commonly assigned U.S.Provisional Patent Application Ser. No. 63/053,107, entitled “HybridPropulsion System Power Management,” filed on Jul. 17, 2020, the entirecontents of which are incorporated herein by reference. Equations (10)and (11) show the derivation of the set point voltages for an energystorage device (V_(B)*) and for a power source (V_(G)*) based on thepower set points, which may be set by user commands. Equation (12) isgeneral power balance relationship between the load, power sources, andenergy storage device.

$\begin{matrix}{V_{B}^{*} = {{P_{B}^{*}D_{B}} + V_{HVDC}}} & (10)\end{matrix}$ $\begin{matrix}{V_{G}^{*} = {{\left( {P_{L} - P_{B}^{*}} \right)\frac{D_{G}}{N_{G}}} + V_{HVDC}}} & (11)\end{matrix}$ $\begin{matrix}{P_{L} = {P_{G1} + P_{G2} + P_{B}}} & (12)\end{matrix}$

The system controller may be configured to calculate load power (P_(L),)using the sum of feedback values from all sources (e.g., power sourcesand energy storage devices), as reported by their local controllers overthe slow communication line. The system controller may be configured tofurther iterate the determination of voltage set points until the powerfeedback from each energy resource is sufficiently close to the targetpower values (e.g., the power set points). This approach may make thesystem more robust to unmeasured parasitic loads and load trackingerrors. However, the system controller may be configured to use feedbackfrom the loads or feedforward from load demands as a feedforward controlterm, for fault detection, and/or as a backup in the event of signalloss (e.g., fault accommodation).

FIG. 5 is a diagram illustrating a voltage deadband for an energystorage device, in accordance with one or more techniques of thisdisclosure. Storage controller 154 shown in FIG. 1 may be configured tooperate the voltage deadband shown in FIG. 5 . The control of the energystorage device includes droop slope 580 for charging and droop slope 582for discharging. The thick line that includes droop slopes 580 and 582is the typical operating line for the storage controller. The voltagedeadband exists at the zero power point in the voltage span betweenmaximum set point 570 and minimum set point 572. Maximum set point 570is the charge-side threshold level, and minimum set point 572 is thedischarge-side threshold level. A storage controller may be configuredto establish or adjust set points 570 and 572 based on command(s)received from a system controller. In some examples, the storagecontroller is configured to change set points 570 and 572 only inresponse to receiving a command received from the system controller.

Battery life diminishes as an energy storage device cycles betweencharging and discharging, which can occur when a storage controlleroperates the energy storage device near zero power without a voltagedeadband. An existing controller would tend to cycle the energy storagedevice between charging and discharging in response to fluctuations insystem voltage. While quick cycling may be desirable in some systems forimmediately responding to power transients, the additional cycle lifeadds undue overdesign, and thus weight, for an aerospace application. Toaddress this, a storage controller may be configured to implement avoltage deadband to control the power converter connected between theenergy storage device and the bus. When the voltage magnitude on the busis within the storage deadband, the storage controller may cause nopower to be released or consumed by the energy storage device. Thestorage controller may be configured to override and/or disable thevoltage loop within the voltage deadband by generating and delivering aconstant zero command to the inner loop.

The storage controller may be configured to determine whether thevoltage magnitude on the bus is outside of the voltage deadband definedby set points 570 and 572. The vertical axis of FIG. 5 represents thebus voltage magnitude sensed by the storage controller. Responsive tosensing that the voltage magnitude on the bus is greater than or equalto maximum set point 570, the storage controller may be configured tocause the energy storage device to charge by receiving an amount ofpower from the bus. Responsive to sensing that the voltage magnitude onthe bus is less than or equal to minimum set point 572, the storagecontroller may be configured to cause the energy storage device todischarge by delivering an amount of power to the bus. The storagecontroller may be configured to determine the amount of charging powerbased on droop slope 580 and the amount of discharging power based ondroop slope 582.

The system controller may be configured to independently adjust no-loadvoltages for charging and discharging, which are represented by maximumset point 570 (V_(BHi)*) and minimum set point 572 (V_(BLo)*), relativeto the original no-load command, V_(B)*, as shown in Equations (14) and(15). The system controller can send indications of the no-load commandsto the storage controller. Vmax and Vmin may be constant values definingthe maximum extent of the voltage range of the deadband. The storagecontroller may be configured to use Equation (13) to implement a voltagedeadband.

$\begin{matrix}{V_{Bref} = \left\{ \begin{matrix}{{V_{BHi}^{*} - {D_{B}P_{B}}},{V_{B} > V_{BHi}^{*}}} \\{V_{B},{V_{BLo}^{*} < V_{B} < V_{BHi}^{*}}} \\{{V_{BLo}^{*} - {D_{B}P_{B}}},{V_{B} < V_{BLo}^{*}}}\end{matrix} \right.} & (13)\end{matrix}$ $\begin{matrix}{V_{BHi}^{*} = \left\{ \begin{matrix}{V_{B}^{*},} & {P_{B}^{*} > 0} \\{{\max\left( {V_{B}^{*},\ V_{\max}} \right)},} & {P_{B}^{*} \leq 0}\end{matrix} \right.} & (14)\end{matrix}$ $\begin{matrix}{V_{BLo}^{*} = \left\{ \begin{matrix}{{\min\left( {V_{B}^{*},\ V_{\min}} \right)},} & {P_{B}^{*} \geq 0} \\{V_{B}^{*},} & {P_{B}^{*} < 0}\end{matrix} \right.} & (15)\end{matrix}$

The system controller can send a command to the storage controller todischarge the energy storage device by increasing the lower thresholdlevel. In response, the storage controller can increase the lowerthreshold of the deadband, which reduces the size of the deadband. Thisis indicated by the dotted lines for P_(B)*≥0 in FIG. 5 . If the lowerthreshold is increased enough, the size of the deadband reaches zero.When the span of the deadband shrinks to zero, as indicated byV_(B)*=Vmax, the storage controller may be configured to operate theenergy storage device in normal droop control with no deadband. In asituation with no deadband, the maximum and minimum set points are thesame: V_(BHi)*=V_(BLo)*=V_(B)*. In other words, shrinking the deadbandto zero may result in a standard, continuous droop curve where only onevoltage magnitude is associated with zero power.

The system controller can send a command to the storage controller tocharge the energy storage device. In response, the storage controllercan decrease the upper threshold of the deadband, which reduces the sizeof the deadband. This reduction is indicated by the dashed lines forP_(B)*≤0 in FIG. 5 . If the upper threshold is lowered far enough, thesize of the deadband reaches zero.

Compared to moving a deadband of fixed size, this approach does notincrease the overall voltage range of the storage controller. Thisapproach may improve stability when power is near zero by reducing thesize of the voltage discontinuity. In contrast, moving a fixed-sizedeadband would increase the range from[−D_(B)×P_(Bmax)<V_(B)<−D_(B)×P_(Bmin)] to[Vmin+D_(B)×P_(Bmin)<V_(B)<Vmax+D_(B)×P_(Bmax)].

The storage controller may be configured to cause the energy storagedevice to release power to the bus in response to determining that thevoltage magnitude on the bus is less than the lower end of the deadband.The storage controller may be configured to cause the energy storagedevice to receive power to the bus in response to determining that thevoltage magnitude on the bus is greater than the upper end of thedeadband. The storage controller can control the power converter and/ora switch network between the power converter and the energy storagedevice.

The maximum deadband voltage range may be approximately equal to theoperating range of the power source(s), expressed by−D_(G)×P_(Gmax)<V_(B)<−D_(G)×P_(Gmin). For example, the target busvoltage may be approximately 1,080 volts, and the span of the voltagedeadband may be approximately ten, twenty, or thirty volts. Thus, thepower source(s) may be configured to supply increased or decreased powerwithin a range of bus voltages defined by the storage deadband (e.g.,before the energy storage device feeds in). When the voltage magnitudeof the bus strays from the target value, the power source(s) may firstfeed in, followed by the energy storage device(s) after the voltagemagnitude crosses a deadband threshold.

Above this range, the deadband can introduce a voltage discontinuitywhere no power source or energy storage device responds to changes inload. However, at or below this range, the deadband just causes devicesto operate sequentially such that the power sources respond to changesin power causing small voltage transients on the bus. In examples inwhich only the energy storage devices respond to changes in power, largevoltage transients may be introduced on the bus. In examples in whichboth the power sources and energy storage devices respond to changes inpower, medium voltage transients may result.

FIG. 6 is a conceptual block diagram illustrating voltage versus currentdroop implementation method, in accordance with one or more techniquesof this disclosure. Energy resource 630 may represent one example ofresource 140, 150, and/or 160 shown in FIG. 1 , and controller 634 mayrepresent one example of controller 144, 154, and/or 164 shown in FIG. 1. Each primary controller (e.g., source controller, storage controller,or load controller) may sense the bus voltage and the output powerdroop. These variables may feed into the outer most control loop of therespective controller. The outer most voltage and droop curve, thevoltage loop, and the inner current or power loop operate based on thelocal measurement points (e.g., sensed current, voltage, and/or power).

In addition, a cable may be connected between the local measurementpoint of energy resource 630 and bus 620. In examples in which the cablelength is too long, the power sharing may be slightly different than anamount determined using an ideal equation due to power dissipation inthe transmission cable. Controller 634 may be configured to address thisissue by switching from a voltage versus output power droop curve to avoltage versus current droop curve.

Distributed energy resource 630 is connected to bus 620 using positiveand negative cables 635A and 635B. Each of cables 635A and 635B includesa built-in resistance 636A and 636B with value of Rn. The terminalvoltage (e.g., local voltage measurement) of energy resource 630 can berepresented as V_(DERn). Current 638A flows from energy resource 630 tobus 620, and current 638B flows from bus 620 to energy resource 630. Thedroop operation that is performed by controller 634 is typically basedon local voltage and current measurements. Equation (16) represents thelocal voltage versus current droop loop effect. Equation (17) is basedon Kirchoff's Voltage Law. Equation (18) results from combining theprevious two equations.V _(DERn) =V _(n) *−D _(n) ×I _(n)  (19)V _(DERn) =V _(HVDC)+2×R _(n) ×I _(n)  (20)V _(HVDC) =V _(n)*−(D _(n)+2R _(n))I _(n) =V _(n) *−D _(neff) ×I_(n)  (21)

The variable D_(neff) relates the voltage magnitude on bus 620 andcurrents 638A and 638B droop in steady-state. Controller 634 mayimplement this loop based on local voltage measurements. Thus, thesystem controller may be configured to also implement the same equationswithout any other modification in the algorithms.

FIG. 7 is a conceptual block diagram illustrating high- and low-voltageenergy storage devices 750H and 750L, in accordance with one or moretechniques of this disclosure. Energy storage device 750H may representone example of energy storage device 150, power converter 752H mayrepresent one example of power converter 152, and storage controller 754may represent one example of storage controller 154 shown in FIG. 1 .Energy storage device 750H may be connected to bus 720 throughconductors 758 and power converter 752H, which may include a DC/DCconverter. Energy storage device 750H may be configured to complementthe main propulsive power generated by a power source (e.g., generator)during the hybrid electric propulsor operating mode. In addition, energystorage device 750L may be configured to complement the reliabilityand/or sustainability of the energy storage device 750H by providing asupplemental power supply to auxiliary load 756, which may include anengine controller (e.g., a full authority digital engine controller),other engine electronics, a fuel pump, a hydraulic pump, and/or anactuator. In examples in which auxiliary load 756 is part of an aircraftengine, the connection to auxiliary load 756 may be separate from thelow-voltage power supply for the airframe of the aircraft. Storagecontroller 754, a load controller, and a source controller are otherexamples of auxiliary load 756 that can receive power from energystorage device 750L and/or from power converter 752L.

Energy storage device 750H may include a high-voltage battery, andenergy storage device 750L may include a low-voltage battery. A no-loadvoltage of energy storage device 750H may be higher than a no-loadvoltage of energy storage device 750L. For example, the no-load voltageof energy storage device 750H may be several hundred volts, and theno-load voltage of energy storage device 750L may be less than onehundred volts. Energy storage device 750L may be configured to deliverpower to bus 720 through power converters 752H and 752L whiledischarging and to receive power from bus 720 through power converters752H and 752L while charging.

In healthy condition, energy storage device 750H may be able to supply asufficient amount of power to auxiliary load 756 through power converter752L. This protocol will also work even if energy storage device 750L isfaulty and disconnected. In response to determining that energy storagedevice 750L is faulty, storage controller 754 may be configured tocontrol power converter 752L to deliver power from energy storage device750H to auxiliary load 756. However, in examples in which both of energystorage devices 750H and 750L are faulty and disconnected, auxiliaryload 756 may still need power to maintain engine operations so thatpropulsive power control capability can be maintained. Even in examplesin which both of energy storage devices 750H and 750L fail, powerconverters 752H and 752L may be configured to continue operating todeliver power from bus 720 to auxiliary load 756. The same controlstrategy will work without any modification if energy storage device750L is healthy and energy storage device 750H is faulty. This will addvalue since flight can be maintained longer after energy storage device750H has failed and energy storage device 750L is live but not burdenedalone.

In examples in which power converter 752H loses the capability ofparticipating in the system-wide control framework because the voltageacross the terminals of energy storage device 750H may not be stable. Ifthe voltage across the terminals of energy storage device 750H is keptwithin a certain voltage range (e.g., 700 to 850 volts), power converter752L may be configured to supply stable output voltage (e.g. 24 volts)for auxiliary load 756 without interruption. In addition, powerconverter 752L may be configured to operate as a buck converter bystepping down the voltage level across conductors 758 and/or across theterminals of energy storage device 750H to a lower voltage level for useby energy storage device 750L and auxiliary load 756.

In a fault condition, power converter 752H may be configured to supplyonly enough power for auxiliary load 756 (e.g., two to four kilowatts),which pushes the operation to discontinuous mode of operation (DCM). InDCM, the efficiency of power converter may fall drastically, as comparedto a normal mode of operation. The control strategy is to control thepower passing through power converter 752H using a voltage control loopfast enough so that storage controller 754 can adjust droop settingsfast enough to regulate the voltage across the terminals of energystorage device 750H within regulated boundaries. The capacitance of aninput capacitor of power converter 752H plays an important role inmaintaining the voltage across the terminals of energy storage device750H.

In the example shown in FIG. 7 , power converter 752L is not directlyconnected to bus 720 but is instead indirectly connected to bus 720through power converter 752H. Although FIG. 7 depicts power converter752L as connected to bus 720 through conductors 758 and power converter752H, in some examples power converter 752L is directly to bus 720. Infurther examples, power converter 752L may be directly connected to bus720 and indirectly connected to bus 720 through power converter 752H.

For example, power converter 752L may be connected to bus 720 and/orpower converter 752H through a network of diodes and switches. Thesearrangements can allow for auxiliary load 756 to receive power from bus720, energy storage device 750H, and/or energy storage device 750L whenthere is a fault somewhere in the system. The fault may occur in one ofthe energy storage devices, in one of the power converters, and/or inthe lines between one of the components in the system. In the event of afault on one or both of energy storage devices 750H and 750L, storagecontroller 754 can communicate an indication of the fault to the systemcontroller, and the system controller may be configured to treat powerconverter 752H as an auxiliary load connected to bus 720. Powerconverter 752H may be configured to operate in buck mode to deliverpower from bus 720 to power converter 752L, which can deliver power toauxiliary load 756. The efficiency of power converters 752H and/or 752Lmay be lower and less consistent during fault operation, as compared toduring normal operation.

FIG. 8A is a conceptual block diagram illustrating a system controllerin the context of a storage fault, in accordance with one or moretechniques of this disclosure. System controllers 810A and/or 810B mayrepresent examples of system controller 110 shown in FIG. 1 . FIG. 8Aalso illustrates the overall control strategy of system controller 810A,particularly in the context of a fault on the electrical lines connectedto an energy storage device. This type of fault can be handled bychanging the control firmware in the high-voltage power converterconnected between the energy storage device and the bus. Systemcontroller 810A may include charging power update module 814A togetherwith set point module 812A without modifying any control loops in theprimary controllers of the energy resources. System controller 810A maybe configured to generate set points based on sensed parameters(voltage, current, power etc. from the power circuit) and user commands(e.g., power and voltage commands from a pilot). The framework shown inFIG. 8A may reduce the number of control algorithms that have to gothrough the qualification and certification process for an aerospaceapplication.

Returning to FIG. 7 , auxiliary load 756 can be modeled as a constantcurrent source. This is manifested as load power Paux in Equations(22)-(24). Due to DCM, the power dissipation caused by power converter752H may be high and unpredictable and is represented as P_(loss) inEquations (22) and (23). Considering global stability, a pure voltageerror square-based positive definite Lyapunov function gives rise toEquation (24). With a sufficiently high value of λ and a known value ofP_(aux), storage controller 754 can implement voltage control withEquation (24). C_(in) represents the capacitance connected acrossconductors 758, ν_(in) represents the voltage across conductors 758,ν_(in)* represents the set point for vin, and λ is a convergingconstant.

$\begin{matrix}{P_{B} = {P_{aux} + P_{loss} + {\frac{d}{dt}\left( {\frac{1}{2}C_{in}v_{in}^{2}} \right)}}} & (22)\end{matrix}$ $\begin{matrix}{P_{B} = {{\lambda C_{in}{v_{in}\left( {v_{in}^{*} - v_{in}} \right)}} + P_{aux} + P_{loss}}} & (23)\end{matrix}$ $\begin{matrix}{P_{B} = {{\lambda C_{in}{v_{in}\left( {v_{in}^{*} - v_{in}} \right)}} + P_{aux}}} & (24)\end{matrix}$

Returning to FIG. 1 , there are two possible modes of operation forsystem 100: default UAC and modified UAC. In the default UAC, systemcontroller 110 may be configured to control source controller 144 andstorage controller 154, while load controller 164 may be independentlycontrolled using, for example, torque control mode. In examples in whichpower source 140 fails and system controller 110 does not receive theinformation indicating the failure due to a slow update rate betweencontrollers 110 and 144, system controller may operate in a blindedoperation mode.

In this situation, the load power may not automatically adjust on itsown causing the voltage magnitude on bus 120 to crash down due to severepower imbalance. This can create a serious problem for emergencyoperations in a hybrid electric propulsion system in an aerospaceapplication. In modified UAC mode of operation, system controller 110 isconfigured to transmit set point commands to load controller 164, aswell as to controllers 144 and 154 to make sure system 100 remainsstable. The voltage control for regulation of bus 120 during faults isimportant, particularly in examples in which voltage magnitude of bus120 goes out of range of a certain value. The propulsors in load 160 maystart malfunctioning, and other controllers 144 and 154 may beconfigured to implement protection schemes in the event of an errant busvoltage.

In the modified UAC mode, system controller 110 may be configured tosend commands to load controller 164. System 100 may include tworectifiers, two propulsors, and an energy storage device may eachimplement the same type of primary control utilizing droop. As comparedto the default UAC, there may not need to be no change in primarycontrol. In addition, each of energy resources 140, 150, and 160 may beconfigured to maintain the stability of the local voltage. One potentialadvantage is that, if one or both rectifiers fail and system controller110 is in blind mode, load controller 164 may be configured totemporarily decide to autonomously and automatically perform a loadshedding operation.

Under the modified UAC, load controller 164 may be configured toautomatically perform a propulsor regenerative operation withoutchanging control mode in power converter 162. Storage controller 154 maybe configured to autonomously control the charging and discharging ofenergy storage device 150. Each of controllers 144, 154, and 164 may beconfigured to automatically decode commands from system controller 110even without any communication among energy resources 140, 150, and 160or controllers 144, 154, and 164.

System 100 may be designed to handle the power capacity of each ofenergy resources 140, 150, and 160, as well as the appropriate powerflow from each of energy resources 140, 150, and 160. For example,controllers 110, 144, 154, and 164 may be configured to manage thecharging and discharging of energy storage device 150, the supply ofpower by power source 140, and load 160 taking power or re-generating.Controllers 110, 144, 154, and 164 may be configured to also control thevoltage magnitude on bus 120 to a desired value.

Equations (25)-(27) show the voltage set points for power source 140,energy storage device 150, and load 160, respectively (V_(G)*, V_(B)*,and V_(P)*). D_(G), D_(B), and D_(P) represent the droop gains of thepower source 140, energy storage device 150, and load 160, respectively.P_(B) represents the power output of energy storage device 150, andP_(L) represents the power consumed by load 160. N_(G) and N_(P)represent the number of generators connected to bus 120 (e.g., as powersource 140) and the number of propulsors connected to bus 120 (e.g., asload 160).

$\begin{matrix}{V_{B}^{*} = {{P_{B}D_{B}} + V_{HVDC}}} & (25)\end{matrix}$ $\begin{matrix}{V_{P}^{*} = {{\frac{P_{L}}{N_{P}}D_{P}} + V_{HVDC}}} & (26)\end{matrix}$ $\begin{matrix}{V_{G}^{*} = {{\frac{\left( {P_{L} - P_{B}} \right)}{N_{G}}D_{G}} + V_{HVDC}}} & (27)\end{matrix}$

FIG. 8B is a conceptual block diagram illustrating a system controller810B for generating a load set point, in accordance with one or moretechniques of this disclosure. Set point module 812B is similar to setpoint module 312 shown in FIG. 3 , except that set point module 812B isconfigured to generate a voltage set point and a droop gain value for aload based on sensed parameters and user commands. In some examples,system controller 810B is configured to implement the modified UACcontrol scheme described herein.

Returning to FIG. 1 , system 100 may experience a failure in powergeneration, which may be caused by a fault in power source 140, powerconverter 142, and/or controller 144. In some examples, energy storagedevice 150 is operating in no-charge/no-discharge mode, and one of powersources 140 is faulty and disconnected. System controller 110 may beconfigured to implement modified UAC using voltage versus current droop.

In the event of a fault in power converter 142, which disconnects powersources 140 from bus 120, load controller 164 may be configured toreduce the power intake of power converter 162 and load 160. Powerconverter 142 may include a rectifier with one or more half-bridgecircuits, where the fault may occur in a switch in a half-bridgecircuit. Even in examples in which power source 140 disconnects from bus120, the voltage magnitude on bus 120 may maintain a target value ifother power sources and energy storage device 150 increase power outputand load 160 decreases power consumption. Under the modified UAC, loadcontroller 164 may be configured to sense a temporary decrease in thevoltage magnitude on bus 120. Responsive to sensing the reducing voltagemagnitude on bus 120, load controller 164 may be configured to controlpower converter 162 to reduce the power consumed by load 160.

Under the modified UAC, system controller 110 can send commands to allof energy resources 140, 150, and 160. As an example, system controller110 may be configured to send power commands to load controller 164, andload controller 164 may be configured to control power converter 162 sothat the power load is shared between multiple loads in a desiredmanner. However, in some examples, system controller 110 may losecommunication with load controller 164 due to, for example, a fault inthe communication line. In examples in which communication is lost, theload commands sent by system controller 110 to load controller 164 willnot arrive at load controller 164, and load 160 will either over satisfyor under-satisfy the load conditions (e.g., supply more or less powerthan selected or commanded by a user).

Load controller 164 may be configured to operate autonomously undermodified UAC by automatically modifying the power consumed by load 160.In doing so, load controller 164 can regulate the voltage magnitude onbus 120 even if the communication between controllers 110 and 164 isdown. This regulation will not only stabilize the voltage magnitude onbus 120, but load controller 164 may be configured to also automaticallyadjust the power consumed by load 160 to maintain the stability whencommunication is lost. In some examples, load controller 164 may beconfigured to reduce a threshold level used for determining when to loadshed in response to determining that a fault has occurred on thecommunication line between controllers 110 and 164.

During blinded operation, controllers 144 and 154 may be configured toset the operating voltages of energy resources 140 and 150 to a baselinelevel to enable power converter 162 to operate autonomously. Forexample, controllers 144 and 154 may be operating with a voltage setpoint for bus 120 that is between 1,020 and 1,140 volts with an enableddeadband for activation or deactivation of energy resources 140 and 150.The baseline level used in situations of communication loss may behigher than the standard operating level to ensure that a sufficientamount of power is delivered to load 160 or lower than the standardoperating level to prevent load 160 from producing an undesirably highlevel of thrust. In examples in which load controller 164 determinesthat the communication is lost, load controller 164 may be configured tooperate power converter 162 in a fully autonomous mode based on thevoltage magnitude on bus 120. In the fully autonomous mode, loadcontroller 164 may operate as a cutback limit controller. Controllers144 and 154 may be configured to operate energy resources 140 and 150 innormal operating modes with power references that are derived so that aremainder of the power is delivered to converter 162. The voltagemagnitude on bus 120 may balance automatically when sufficient power isdelivered by power converters 142 and 152.

In examples in which communication is lost between controllers 110 and164, system controller 110 may be configured to cause load 160 to drawmore power from bus 120 by sending commands to controllers 144 and 154to increase the voltage set points for bus 120. Load controller 164 maybe configured to implement an upper threshold level for increasing thepower drawn by load 160 in response to determining that communicationwith system controller 110 has been lost. Thus, system controller 110can increase the propulsion generated by load 160 by adjusting the setpoints used by controllers 144 and 154, which will cause an increase inthe voltage magnitude on bus 120. Load controller 164 can determinewhether the increased bus voltage is greater than the upper thresholdlevel when communication has been lost and increase the power drawn byload 160 in response to determining that the bus voltage is greater thanthe upper threshold level.

Load controller 164 may be configured to maintain the power drawn bypower converter 162 as the voltage magnitude on bus 120 increases beyondan upper threshold level. However, in examples in which load 160 isoperating below a maximum rated power, load controller 164 may beconfigured to increase the power drawn by power converter 162 inresponse to determining that the voltage magnitude on bus 120 is greaterthan a first upper threshold level. The first upper threshold level maybe less than the power rating that represents a hard cap on theoperation of load 160.

System controller 110 may be configured to also cause load 160 to drawless power from bus 120 by sending commands to controllers 144 and 154to reduce the voltage set points for bus 120. Thus, system controller110 can decrease the propulsion generated by load 160 by decreasing thevoltage magnitude on bus 120. Responsive to determining thatcommunication is lost between controllers 110 and 164, load controller164 may be configured to reduce the threshold level for load shedding sothat controllers 110, 144, and 154 can more easily cause a reduction inthrust by load 160. For example, controllers 144 and 154 can reduce thepower being supplied to bus 120 to cause a reduction in bus voltagebelow the reduced threshold level being implemented by load controller164.

System controller 110 may be configured to store the previous set pointssent to load controller 164 in response to determining that thecommunication between controllers 110 and 164 has been lost. Systemcontroller 110 can use these previous set points to determine new setpoints for controllers 144 and 154. System controller 110 may beconfigured to iteratively determine the set points for controllers 144and 154 based on newly sensed parameters until the actual power valuesfor power converters 142, 152, and 162 are within an acceptable range.

Additionally or alternatively, there may be no change in load controller164 but controllers 144 and 154 may be configured to set base voltagesbelow deadband. As one example, controllers 144 and/or 154 can changethe deadband range to between 980 volts and 1,020 volts. Controller 164may be configured to operate a cutback limit controller to automaticallyadjust the power level consumed by load 160. System 100 may have N+1redundancy in source and loads, which makes autonomous operate feasiblewith this control strategy.

In examples in which load controller 164 is not under the UAC controlframework (e.g., not configured to receive set point commands fromsystem controller 110), load controller 164 may be configured toimplement a separate reduction curve for the motor power referenceversus the voltage magnitude on bus 120. Load controller 164 may beconfigured to implement this control strategy only in response todetermining that the voltage magnitude on bus 120 is less than athreshold level. For example, the voltage magnitude on bus 120 maysuddenly fall due to an imbalance in power generation and powerutilization. In examples in which storage controller 154 is using avoltage deadband, storage controller 154 may be configured to causeenergy storage device 150 to release power to bus 120 only in responseto determining that the voltage magnitude on bus 120 is less than athreshold level.

Using default UAC, power converters 142 and 152 are under the UACcontrol framework, but power converter 162 is not under the UAC controlframework. Load controller 164 may be configured to implement a loadshed algorithm. As an example, a fault and disconnection may occur inpower converter 142, while a second power source remains connected tobus 120. Before the time that the fault occurs, both of the powersources were operating at full capacity. At the time that the faultoccurs, energy storage device 150 may operate in no-charge/no-dischargemode. In response to determining that the voltage magnitude on bus 120is less than a threshold level just after the fault occurs, loadcontroller 164 may be configured to reduce the power drawn to load 160by power converter 162. Load controller 164 may be configured to operatea load reduction loop under the default UAC arrangement, where the loadreduction loop includes a threshold level below the desired voltagemagnitude on bus 120.

Although load controller 164 can properly implement this load sheddingalgorithm, the load shedding reduces the power drawn by load 160 usingan open loop control. This operation by load controller 164 maystabilize the voltage magnitude on bus 120 at a level lower than theoriginally rate value, but the voltage magnitude on bus 120 may notachieve the originally rated value.

FIG. 9 is a conceptual block diagram illustrating a charging circuit 970for two energy storage devices 950A and 950B, in accordance with one ormore techniques of this disclosure. Energy storage devices 950A and/or950B may represent examples of energy storage device 150 shown in FIG. 1. When an aircraft is grounded, energy storage devices 950A and 950B canbe charged using charging circuit 970. As shown in FIG. 9 , chargingcircuit 970 can include a current source which can charge energy storagedevices 950A and 950B at a certain voltage level across the terminals ofenergy storage devices 950A and 950B (e.g., one thousand volts).However, often when HVDC battery is fully discharged the voltage of thebattery can vary over a range but much lower than battery chargedvoltage (e.g. 670V to 850V). Thus, the charging of energy storagedevices 950A and 950B can be done using UAC.

Charging circuit 970 may be configured to charge energy storage devices950A and 950B with a constant current. The voltage magnitude of bus 920can be maintained at a specific level to make sure that charging circuit970 works in order. The number of energy storage devices to be chargedis represented by N_(B), and the power flowing out of each of energystorage devices 950A and 950B can be represented as Equation (28). Theno-load voltage of the droop curve is to be V_(B)* and droop gain ofeach of energy storage devices 950A and 950B can be represented byD_(B). Equation (29) shows the droop formula for each energy storagedevice. Equation (30) shows the voltage set point for energy storagedevices 950A and 950B to initiate the storage controllers.

$\begin{matrix}{P_{B1} = {P_{B2} = {- \frac{V_{HVDC} \times I_{charger}}{N_{B}}}}} & (28)\end{matrix}$ $\begin{matrix}{V_{HVDC} = {V_{B}^{*} - {D_{B} \times P_{B}}}} & (29)\end{matrix}$ $\begin{matrix}{V_{B}^{*} = {V_{HVDC} - {D_{B} \times \frac{V_{HVDC} \times I_{charger}}{N_{B}}}}} & (30)\end{matrix}$

A storage controller implementing these control techniques may beconfigured to charge energy storage devices 950A and 950B of a hybridelectric propulsion system using charging circuit 970. In addition, thestorage controller may be able to maintain a specific voltage magnitudeon bus 920 to make charging circuit 970 function properly.Alternatively, if charging circuit 970 can be operated in constantvoltage mode, ground charging can be performed in a manner that issimilar to normal operation in UAC. The storage controller(s) may beconfigured to independently set each DC/DC converter that is connectedbetween bus 920 and a respective one of energy storage devices 950A and950B to a charge rate by setting the no-load voltage above a nominalvoltage. In addition, charging circuit 970 can automatically provide thetotal power required to maintain the voltage magnitude on bus 920.

FIGS. 10A and 10B are plots illustrating a change in a set point, inaccordance with one or more techniques of this disclosure. In theexample shown in FIG. 10A, the system controller sends a new set pointcommand to the primary controller (e.g., a source controller). Inresponse to receiving the new set point command from the systemcontroller, the primary controller causes shift 1030A from droop curve1040A to droop curve 1042A. Shift 1030A results in increase 1050A of thereference point for the voltage magnitude on the bus. To increase thebus voltage, the primary controller increases the power generated by thepower source and supplied to the bus, as shown by increase 1060A. As thepower generated by the power source increases, the voltage referencepoint decreases down droop curve 1042B until the bus voltage and thepower reach an equilibrium.

In the example shown in FIG. 10B, the bus voltage experiences decrease1000B due to an external event, such as an increase in power consumptionby a load or a reduction in power supply by a source. The primarycontroller may be configured to seek the voltage reference point ondroop curve 1040B by increasing power, as shown by increase 1010B. Asthe primary controller increases power along increase 1010B, the voltagereference point decreases along line 1020B until the voltage and powerreach an equilibrium. The system controller then sends a new set pointcommand to the primary controller. In response to receiving the new setpoint command from the system controller, the primary controller causesshift 1030B from droop curve 1040B to droop curve 1042B. Shift 1030Bresults in increase 1050B of the reference set point for the voltagemagnitude on the bus. To increase the bus voltage, the primarycontroller temporarily increases the power generated by the power sourceand supplied to the bus, which causes the voltage magnitude on the busto increase, as shown by increase 1060B. Eventually, power and voltagereach an equilibrium along droop curve 1042B.

One technique for increasing the power generated by a power source is toincrease the set point for the voltage magnitude on the bus. The sourcecontroller may be configured to increase the power generated andsupplied to the bus in order to increase the voltage magnitude on thebus to the reference point. For each iteration, the source controllermay be configured sense the current power generation by the powersource, to update the voltage reference point based on the most recentlysensed power generation, and to adjust the power generated by the powersource to achieve the voltage reference point. For the next iteration,the source controller can update the voltage reference point based on anewly sensed power generation.

FIG. 11 is a flowchart illustrating an example process for operating asystem controller, in accordance with one or more techniques of thisdisclosure. The techniques of FIG. 11 are described with reference tosystem controller 110 shown in FIG. 1 , but the techniques of FIG. 11may be performed by either of system controllers 310, 810A, and 810Bshown in FIGS. 3, 8A, and 8B.

In the example of FIG. 11 , system controller 110 determines a first setpoint for power converter 142 that is connected between bus 120 andpower source 140 (1100). System controller 110 may receive a sensedsignal indicating the voltage magnitude on bus 120, where the voltagemagnitude may represent the difference in voltages on two differentialrails of bus 120. System controller 110 may determine the set pointbased on the voltage magnitude on bus 120, along with other parameterssuch as the desired propulsion to be produced by load 160 and the powerdrawn or produced by each of energy resources 140, 150, and 160.

In the example of FIG. 11 , system controller 110 determines a secondset point for power converter 152 that is connected between bus 120 andenergy storage device 150 (1102). For example, system controller 110 maybe configured to determine whether energy storage device 150 shouldoperate in charging mode, discharging mode, and/or a mode withoutcharging or discharging. System controller 110 may be configured to alsodetermine whether energy storage device 150 should have a deadband andif so, determine the lower and upper limits of the voltage deadband.

In the example of FIG. 11 , system controller 110 transmits anindication of the first set point to source controller 144 (1104).Source controller 144 may be configured to set or adjust a droop curvebased on the set point received from system controller 110. For example,source controller 144 may be configured to increase the power generatedby power source 140 in response to receiving a higher voltage set pointfor bus 120 from system controller 110. Source controller 144 may beconfigured to increase the power generated by power source 140 toachieve the new set point by pushing the bus voltage higher.

In the example of FIG. 11 , system controller 110 transmits anindication of the second set point to storage controller 154 (1106).Storage controller 154 may be configured to set or adjust a droop curvebased on the set point received from system controller 110. For example,storage controller 154 may be configured to increase change the powerdischarge energy storage device 150 in response to receiving a highervoltage set point for bus 120 from system controller 110. Sourcecontroller 144 may be configured to increase the power generated bypower source 140 to achieve the new set point by pushing the bus voltagehigher.

FIG. 12 is a flowchart illustrating an example process for operating astorage controller, in accordance with one or more techniques of thisdisclosure. In the example of FIG. 12 , storage controller 154determines that a voltage magnitude on bus 120 is less than a firstthreshold level in a first instance (1200). Storage controller 154 mayreceive a sensed signal indicating the voltage magnitude on bus 120. Thefirst threshold level may represent the lower limit of a deadbandimplemented by storage controller 154. Storage controller 154 may beconfigured to set the first threshold level based on a command receivedby storage controller 154 from system controller 110.

In the example of FIG. 12 , storage controller 154 causes energy storagedevice 150 to deliver power through power converter 152 to bus 120 inresponse to determining that the voltage magnitude on bus 120 is lessthan the first threshold level in the first instance (1202). Storagecontroller 154 may be configured to determine the amount of power forenergy storage device 150 to deliver to bus 120 based on the voltagemagnitude on bus 120 and further based on a droop curve that is storedto a memory coupled to storage controller 154. As the voltage magnitudeon bus 120 decreases below the first threshold level, storage controller154 may be configured to further increase the power delivered by energystorage device 150 to bus 120.

Storage controller 154 may be configured to determine a first magnitudeof power being delivered by energy storage device 150 to bus 120 in thefirst instance. Storage controller 154 can determine the power beingdelivered by determining the current and voltage through power converter152 and multiplying the current and voltage. Storage controller 154 maybe configured to then determine a voltage reference point based on thefirst magnitude of power being delivered by energy storage device 150.The voltage reference point may be higher than the sensed voltagemagnitude on bus 120. Storage controller 154 may be configured to alsocause energy storage device 150 to deliver a second magnitude of powerto bus 120 in response to determining that the voltage magnitude on bus120 is less than the voltage reference point, wherein the secondmagnitude of power is greater than the first magnitude of power. Thus,storage controller 154 may increase the power output of energy storagedevice 150 to attain the voltage reference point for bus 120.

Storage controller 154 may be configured to determine a third magnitudeof power being delivered by energy storage device 150 to bus 120 in athird instance after causing energy storage device 150 to deliver thesecond magnitude of power. Storage controller 154 may be configured tothen determine a second voltage reference point based on the thirdmagnitude of power being delivered by energy storage device 150. Thesecond voltage reference point may be lower than the original referencepoint, especially if the third magnitude of power is greater than thefirst magnitude of power, because the droop curve may associate higherpower magnitudes with lower reference points.

In the example of FIG. 12 , storage controller 154 determines that thevoltage magnitude on bus 120 is greater than the first threshold levelin a second instance (1204). The second threshold level may representthe upper limit of a deadband implemented by storage controller 154.Storage controller 154 may be configured to set the second thresholdlevel based on a command received by storage controller 154 from systemcontroller 110.

In the example of FIG. 12 , storage controller 154 causes energy storagedevice 150 to receive power through power converter 152 from bus 120 inresponse to determining that the voltage magnitude on bus 120 is greaterthan the first threshold level in the second instance (1206). Storagecontroller 154 may be configured to determine the amount of power forenergy storage device 150 to receive from bus 120 based on the voltagemagnitude on bus 120 and further based on a droop curve that is storedto a memory coupled to storage controller 154. As the voltage magnitudeon bus 120 increases above the second threshold level, storagecontroller 154 may be configured to further increase the power receivedby energy storage device 150 from bus 120.

In response to determining that the voltage magnitude on bus 120 isbetween the first and second threshold levels, storage controller 154may be configured to cause energy storage device 150 to refrain fromdischarging or charging. The voltage range between the first and secondthreshold levels is a voltage deadband, such that energy storage device150 neither charges nor discharges when the voltage magnitude on bus 120is in the voltage deadband. System controller 110 may be configured toset the limits of the deadband by sending commands to storage controller154.

The extent of the storage deadband, which may be defined as the secondthreshold level minus the first threshold level, may be nearly as largeas the operating range of power source 140. For example, the extent ofthe storage deadband may be at least fifty, sixty, seventy, eighty, orninety percent of the operating range of power source 140. The extent ofthe storage deadband may be less than or equal to the operating range ofpower source 140 so that energy storage device 150 kicks in before powersource 140 reaches the upper limit of an operating range. Having astorage deadband that is almost as large as the operating range of powersource 140 may reduce the cycling and fatigue experienced by energystorage device 150 without any gaps where energy resources 140 and 150cannot support the power draw of load 160.

FIG. 13 is a flowchart illustrating an example process for operating aload controller, in accordance with one or more techniques of thisdisclosure. In the example of FIG. 13 , load controller 164 determinesthat a voltage magnitude on bus 120 is not less than a threshold levelin a first instance (1300). Load controller 164 can determine thethreshold level based on a command received from system controller 110.The threshold level may be a voltage magnitude below which loadcontroller 164 reduces the power drawn by load 160.

Load controller 164 then causes power converter 162 to deliver a firstmagnitude of power to load 160 in response to determining that thevoltage magnitude on bus 120 is not less than the threshold level in thefirst instance (1302). The first magnitude of power may be a defaultlevel of power based on user input or a command from system controller110. The droop curve for bus voltages above the threshold level may beflat, such that load 160 and power converter 162 draw a constant amountof power for voltages greater than the threshold level.

In the example of FIG. 13 , load controller 164 determines that thevoltage magnitude on bus 120 is less than the threshold level in asecond instance (1304). Load controller 164 causes power converter 162to deliver a second magnitude of power to load 160 in response todetermining that the voltage magnitude on bus 120 is less than thethreshold level in the second instance (1306). The second magnitude ofpower is less than the first magnitude of power, which can serve tostabilize the voltage magnitude on bus 120 in the second instance. Asthe voltage magnitude on bus 120 decreases, load controller 164 may beconfigured to reduce the power drawn by power converter 162. In examplesin which the voltage magnitude on bus 120 is below a lowest thresholdlevel, load controller to reduce the power drawn by power converter 162to zero.

Load controller 164 may be configured to determine a voltage referencepoint based on the magnitude of power being drawn by load 160 or bypower converter 162. For example, load controller 164 may use a droopcurve to determine a voltage reference point associated with themagnitude of power being drawn by load 160. Load controller may thendetermine whether to increase or decrease the power delivered by powerconverter 162 to load 160 in response to determining whether the voltagereference point is greater than or less than the current voltagemagnitude on bus 120. Responsive to determining that the current voltagemagnitude on bus 120 is less than the voltage reference point, loadcontroller 164 may be configured to cause power converter 162 to reducethe power being delivered to load 160 to raise the bus voltage to thevoltage reference point. As used herein, a set point may refer to athreshold level at the edge of a deadband, and a reference point mayrefer to a point on a droop curve that is outside of the deadband.

Load controller 164 may be configured to perform load shedding byenabling a droop curve to reduce the power drawn by load 160 as thevoltage magnitude on bus 120 decreases. Each reduction in bus voltagecan result in a lowered power draw by power converter 162 and load 160.In examples in which the voltage magnitude on bus 120 drops below athreshold level, load controller 164 may be configured to disconnectload 160 from bus 120. Load controller 164 may be configured to alsoreceive an updated command from system controller 110 to increase orreduce the threshold level for load shedding. Responsive to determiningthat the voltage magnitude on bus 120 is less than the new thresholdlevel, load controller 164 may be configured to cause power converter162 to reduce the power being delivered to load 160 from the magnitudeof power that was being delivered to load 160 before the arrival of theupdated command from system controller 110.

Load shedding (e.g., decreasing the power drawn by load 160) mayincrease the voltage magnitude on bus 120. In examples in which system100 includes two propulsors, an operator may provide an input forreduced propulsion from a first propulsor. System controller 110 may beconfigured to transmit an indication of an increased voltage referencepoint to load controller 164, which may cause load controller 164 toreduce the power drawn by a motor driving the first propulsor.

The reduced power draw may result in an increased voltage magnitude onbus 120. If a second load controller is configured to operate the secondpropulsor on a droop curve, the second load controller may be configuredto increase the power drawn by the second propulsor in response tosensing the increased voltage magnitude on bus 120. This situation mayresult in an uncommanded increase in thrust from the second propulsorafter the operator commands a reduction in thrust from the firstpropulsor. To avoid an uncommanded increase in thrust on the high end ofbus voltages, load controller 164 may be configured to implement adeadband.

By implementing the deadband, load controller 164 may not cause anincrease in the power drawn by power converter 162 and load 160 when thevoltage magnitude on bus 120 increases above a certain voltage level.However, on the low end of voltage magnitudes for bus 120, loadcontroller 164 may be configured to reduce the power drawn by load 160to reduce the likelihood that the voltage magnitude on bus 120collapses.

In normal operation, system controller 110 may be configured to controlthe operation of load controller 164 by transmitting set point commandsto load controller 164. Responsive to receiving a set point command fromsystem controller 110, load controller 164 may be configured to enabledroop control. Responsive to determining that a set point command hasnot been received from system controller 110 for a particular timeduration, load controller 164 may be configured to disable droopcontrol. Even in examples in which communication is lost betweencontrollers 110 and 164, system controller 110 may be able to controlthe operation of load controller 164 by controlling the voltagemagnitude on bus 120 through controllers 144 and 154.

Thus, responsive to determining that communication has been lost withsystem controller 110, load controller 164 may be configured to enabledroop control to allow for system controller 110 to issue thrustcommands via the voltage magnitude on bus 120. Responsive to determiningthat communication with system controller 110 has been lost, loadcontroller 164 may be configured to implement an upper threshold levelfor the voltage magnitude on bus 120 above which load controller 164will increase the power drawn by load 160. Between the upper and lowerthreshold levels, load controller 164 may be configured to refrain fromincreasing or decreasing the power drawn by load 160 in response tochanges in the voltage magnitude on bus 120.

Both of controllers 110 and 164 may store data indicating the droopcurve(s) to be implemented by load controller 164, so even aftercommunication loss, system controller 110 can effectively cause anincrease or reduction in thrust by increasing or decreasing the voltagemagnitude on bus 120. For example, in response to determining a loss incommunication, load controller 164 may be configured to implement thelast droop curve transmitted by system controller 110 before the loss incommunication and/or to implement a default droop curve stored in localmemory.

FIG. 14 is a flowchart illustrating an example process for operating asystem controller based on user input, in accordance with one or moretechniques of this disclosure. In the example of FIG. 14 , systemcontroller 110 receives user input from an operator of system 100(1400). For example, the operator can adjust the throttle setting in thecockpit of an aircraft, and the avionics system will then transmit anindication of this adjustment to system controller 110. The operator mayalso be able to adjust the share of power that comes from energy storagedevice 150. System controller 110 can receive an indication of thisrequest by the user for increased or reduced propulsion in system 100.Thus, the user input received by system controller 110 may indicate thatthe user has changed a setting or parameter controlled by the user.

System controller 110 then determines a new set point for one of energyresources 140, 150, and 160 based on the user input (1402). The setpoint may include a target value for the voltage magnitude on bus 120,an upper deadband threshold level, and/or a low deadband thresholdlevel. Additionally or alternatively, the set point be a torque setpoint for load 160. In the example of FIG. 14 , system controller 110transmits an indication of the new set point to one of controllers 144,154, and 164 (1404). System 100 may include a wired communication lineand/or a wireless communication channel between system controller 110and each of controllers 144, 154, and 164 for sending set pointcommands.

In the example of FIG. 14 , system controller 110 senses a change in apower level of an energy resource caused by the respective one ofcontrollers 144, 154, and 164 implementing the new set point (1406).System controller 110 may be configured to determine that a change inpower level has occurred by determining the power conducted by one ofpower converters 142, 152, and 162 before and after implementing the newset point.

A primary controller can cause a change in power level by increasing ordecreasing the power received from bus 120 or delivered to bus 120.System controller 110 then determines a second set point for therespective energy resource based on the change in the power level of theenergy resource and further based on the user input (1408). The secondset point may essentially reset the droop slopes implemented bycontrollers 144, 154, and 164. In determining the second set point,system controller 110 may be configured to account for the change involtage magnitude on bus 120 after the primary controller implementedthe first set point. System controller 110 may be configured to transmitthe second set point to load controller 164 in response to determiningthat the voltage magnitude on bus 120 has not reached a steady statevalue. System controller 110 may be configured to then wait for anotherinput from the user after transmitting the second set point to loadcontroller 164.

One of controllers 110, 144, 154, and 164 may be configured to determinewhether the rate of change of a set point is greater than or equal to athreshold rate. In response to determining that the rate of change isgreater than or equal to the threshold rate, the controller may beconfigured to shrink a deadband to zero and wait for the voltagemagnitude on bus 120 to achieve an equilibrium level. In response todetermining that the voltage magnitude on bus 120 has achieved anequilibrium level, the controller may add a deadband to the droopcontrol.

The following numbered examples demonstrate one or more aspects of thedisclosure.

Example 1. A method includes determining, by a system controller, afirst set point for a first power converter connected to a bus, wherethe first power converter has a first topology. The method also includestransmitting, by the system controller, an indication of the first setpoint to a source controller, where the source controller is configuredto control the first power converter. The method further includesdetermining, by the system controller, a second set point for a secondpower converter connected to the bus, where the second power converterhas a second topology, and the first topology being different from thesecond topology. The method includes transmitting, by the systemcontroller, an indication of the second set point to a storagecontroller, where the storage controller is configured to control thesecond power converter.

Example 2. The method of example 1, further including determining athird set point for a third power converter connected between a load andthe bus.

Example 3. The method of example 2, where a topology of the third powerconverter is different from the second topology.

Example 4. The method of the preceding examples or any combinationthereof, further including transmitting an indication of a third setpoint to a load controller.

Example 5. The method of the preceding examples or any combinationthereof, further including receiving an indication that a user hasrequested a change in propulsion.

Example 6. The method of the preceding examples or any combinationthereof, further including transmitting a set point to a load controllerin response to receiving the indication that the user has requested thechange in the propulsion.

Example 7. The method of the preceding examples or any combinationthereof, further including transmitting a second voltage command to theload controller indicating a new value for the threshold level inresponse to determine that the voltage magnitude on the bus has notreached the steady state.

Example 8. A method includes determining, by a storage controller, thata voltage magnitude on a bus is less than a first threshold level in afirst instance. The method also includes causing, by the storagecontroller, an energy storage device to deliver power to the bus inresponse to determining that the voltage magnitude on the bus is lessthan the first threshold level. The method further includes determining,by the storage controller, that the voltage magnitude on the bus isgreater than a second threshold level in a second instance, where thesecond threshold level is greater than the first threshold level. Themethod includes causing, by the storage controller, the energy storagedevice to receive power from the bus in response to determining that thevoltage magnitude on the bus is greater than the second threshold level.

Example 9. The method of example 8, further including causing the energystorage device to refrain from discharging or charging in response todetermining that the voltage magnitude on the bus is within a voltagedeadband defined between the first threshold level and the secondthreshold level.

Example 10. The method of example 9, where an extent of the voltagedeadband is greater than fifty, sixty, seventy, or eighty percent of anoperating range of the power source.

Example 11. The method of example 9 or example 10, where the extent ofthe voltage deadband is less than or equal to the operating range of thepower source.

Example 12. The method of examples 8-11 or any combination thereof,further including receiving a voltage command from a system controller.

Example 13. The method of examples 8-12 or any combination thereof, setthe first threshold level based on a voltage command received from asystem controller.

Example 14. The method of examples 8-13 or any combination thereof,further including setting a droop curve for discharge of the energystorage device based on a voltage command received from a systemcontroller.

Example 15. The method of examples 8-14 or any combination thereof,further including setting the second threshold level based on a voltagecommand received from a system controller.

Example 16. The method of examples 8-15 or any combination thereof,further including determining a first magnitude of power being deliveredby the energy storage device to the bus in the first instance.

Example 17. The method of examples 8-16 or any combination thereof,further including determining a voltage reference point based on thefirst magnitude of power being delivered by the energy storage device.

Example 18. The method of examples 8-17 or any combination thereof,further including causing the energy storage device to deliver a secondmagnitude of power to the bus in response to determining that thevoltage magnitude on the bus is less than a voltage reference point,where the second magnitude of power is greater than a first magnitude ofpower previously delivered by the energy storage device.

Example 19. The method of examples 8-18 or any combination thereof,further including determining a third magnitude of power being deliveredby the energy storage device to the bus in a third instance after thefirst instance.

Example 20. The method of examples 8-19 or any combination thereof,further including determining a second voltage reference point based onthe third magnitude of power being delivered by the energy storagedevice, where the second voltage reference point is different from thefirst voltage reference point.

Example 21. The method of examples 8-20 or any combination thereof,further including determining a fault on a low-voltage energy storagedevice.

Example 22. The method of examples 8-21 or any combination thereof,further including controlling the second power converter to deliverpower from the first energy storage device to the storage controller inresponse to determining the fault on the second energy storage device.

Example 23. A method includes determining, by a load controller, that avoltage magnitude on a bus is not less than a threshold level in a firstinstance. The method also includes causing, by a load controller, apower converter to deliver a first magnitude of power to the load inresponse to determining that the voltage magnitude on the bus is notless than the threshold level in the first instance. The method furtherincludes determining that the voltage magnitude on the bus is less thanthe threshold level in a second instance. The method includes causingthe power converter to deliver a second magnitude of power to the loadin response to determining that the voltage magnitude on the bus is lessthan the threshold level in the second instance, the second magnitude ofpower being less than the first magnitude of power.

Example 24. The method of example 23, further including receiving afirst voltage command from a system controller.

Example 25. The method of example 23 or example 24, further includingsetting the threshold level based on a first voltage command receivedfrom a system controller.

Example 26. The method of examples 23-25 or any combination thereof,further including determining a fault on a communication line betweenthe load controller and a system controller.

Example 27. The method of examples 23-26 or any combination thereof,further including controlling the power converter to operate in anautonomous mode in response to determining a fault on a communicationline between the load controller and a system controller.

Example 28. The method of examples 23-27 or any combination thereof,further including reducing a value of the threshold level in response todetermining a fault on a communication line between the load controllerand a system controller.

Example 29. The method of examples 23-28 or any combination thereof,further including implementing a second threshold level in response todetermining a fault on a communication line between the load controllerand a system controller, where the second threshold level is greaterthan the first threshold level.

Example 30. The method of examples 23-29 or any combination thereof,further including determining that the voltage magnitude on the bus isgreater than the second threshold level in a third instance.

Example 31. The method of examples 23-30 or any combination thereof,further including causing the power converter to deliver a thirdmagnitude of power to the load in response to determining that thevoltage magnitude on the bus is greater than the second threshold levelin the third instance, where the third magnitude of power is greaterthan the first magnitude of power.

Example 32. The method of examples 23-31 or any combination thereof,further including setting the threshold level to a first value based onthe first voltage command; receiving a second voltage command from thesystem controller; and setting the threshold level to a second valuebased on the second voltage command, where the second value is greaterthan the first value.

Example 33. The method of examples 23-32 or any combination thereof,further including causing the power converter to deliver a thirdmagnitude of power to the load in response to setting the thresholdlevel to the second value, where the third magnitude of power is lessthan the second magnitude of power.

Example 34. The method of examples 23-33 or any combination thereof,further including determining a voltage reference point based on thesecond magnitude of power being delivered to the load in the secondinstance; and causing the power converter to deliver a third magnitudeof power to the load in response to determining that the voltagemagnitude on the bus is less than the voltage reference point, where thethird magnitude of power is less than the second magnitude of power.

Example 35. The method of examples 23-34 or any combination thereof,further including receiving at least one sensed signal indicating acurrent through the load or a voltage across the load.

Example 36. The method of examples 23-35 or any combination thereof,further including determining a magnitude of power being delivered tothe load based on at least one sensed signal.

Example 37. The method of examples 23-36 or any combination thereof,further including operating a current loop to generate control signalsfor the power converter.

Example 38. The method of examples 23-37 or any combination thereof,where the power converter includes an inverter configured to convertdirect-current electricity on the bus to alternating-current electricityto drive a motor.

Example 39. A device includes a computer-readable medium havingexecutable instructions stored thereon, configured to be executable byprocessing circuitry for causing the processing circuitry to perform themethod of examples 1-38 or any combination thereof.

Example 40. A system including means for performing each of the methodsteps of examples 1-38 or any combination thereof.

Example 41. A system including a bus and a first power converterconnected to the bus. The system also includes a second power converterconnected to the bus, the second power converter having a topologydifferent from the topology of the first power converter. The systemfurther includes a power source and an energy storage device connectedto the bus via the first and second power converters, respectively. Inaddition, the system includes a source controller configured to controlthe first power converter and a storage controller configured to controlthe second power converter. The system also includes a system controllerconfigured to determine a first set point for the first power converter,transmit an indication of the first set point to the source controller,determine a second set point for the second power converter, andtransmit an indication of the second set point to the storagecontroller.

Example 42. The system of example 41, where the system controller isconfigured to perform each of the method steps of examples 1-7 or anycombination thereof.

Example 43. The system of example 41 or example 42, further including athird power converter, a load configured to receive power from the busvia the third power converter, and a load controller configured tocontrol the third power converter.

Example 44. The system of examples 41-43 or any combination thereof,where a third power converter connected between the bus and a loadincludes a third topology, the second topology being different from thethird topology.

Example 45. The system of examples 41-44 or any combination thereof,where a load connected to the bus via a power converter includes apropulsor.

Example 46. The system of examples 41-45 or any combination thereof,further including a motor configured to drive a propulsor based on powerreceived from the bus via a third power converter.

Example 47. The system of examples 41-46 or any combination thereof,further including an inverter configured to convert direct-currentelectricity on the bus to alternating-current electricity to drive amotor.

Example 48. The system of examples 41-47 or any combination thereof,where the power source includes a generator that is coaxial with anengine shaft.

Example 49. The system of examples 41-48 or any combination thereof,where the first power converter includes a rectifier.

Example 50. The system of examples 41-49 or any combination thereof,where the second power converter includes a direct current/directcurrent converter.

Example 51. The system of examples 41-50 or any combination thereof,further including a second energy storage device connected to the powerconverter, where the energy storage device is configured to providepower to the auxiliary load.

Example 52. A system includes an energy storage device configured todeliver power to a bus or receive power from a bus via a powerconverter. The system also includes a controller configured to determinethat a voltage magnitude on the bus is less than a first threshold levelin a first instance and cause the energy storage device to deliver powerto the bus in response to determining that the voltage magnitude on thebus is less than the first threshold level. The controller is alsoconfigured to determine that the voltage magnitude on the bus is greaterthan a second threshold level in the second instance, where the secondthreshold level is greater than a first threshold level and cause theenergy storage device to receive power from the bus in response todetermining that the voltage magnitude on the bus is greater than thesecond threshold level.

Example 53. The system of examples 41-52 or any combination thereof,further including a load controller configured to perform each of themethod steps of examples 23-38 or any combination thereof.

Example 54. The system of examples 41-53 or any combination thereof,where an extent of a voltage deadband of the energy storage device isgreater than sixty percent of an operating range of a power source inthe system.

Example 55. The system of examples 41-54 or any combination thereof,where the extent of a voltage deadband of the energy storage device isless than or equal to the operating range of a power source in thesystem.

Example 56. The system of examples 41-55 or any combination thereof,where the energy storage device includes a high-voltage energy storagedevice connected to the bus via a high-voltage power converter.

Example 57. The system of examples 41-56 or any combination thereof,further including a low-voltage power converter connected to thehigh-voltage energy storage device.

Example 58. The system of examples 41-57 or any combination thereof,further including a low-voltage energy storage device connected to thebus through a low-voltage power converter and a high-voltage powerconverter.

Example 59. The system of examples 41-58 or any combination thereof,further including one or more conductors connected between thehigh-voltage energy storage device and the high-voltage power converter,where the low-voltage power converter is connected to the one or moreconductors.

Example 60. The system of examples 41-59 or any combination thereof,where the second power converter includes a buck converter configured togenerate a stepped-down voltage signal based on electricity receivedfrom the one or more conductors.

Example 61. The system of examples 41-60 or any combination thereof,where the second energy storage device is configured to receive thestepped-down voltage signal from the second power converter.

Example 62. The system of examples 41-61 or any combination thereof,where the second power converter is not directly connected to the bus.

Example 63. The system of examples 41-62 or any combination thereof,where the low-voltage energy storage device is configured to deliverpower to the bus via the second power converter and via the first powerconverter in a third instance.

Example 64. The system of examples 41-63 or any combination thereof,where the low-voltage energy storage device is configured to receivepower from the bus via the first power converter and via the secondpower converter in a fourth instance.

Example 65. The system of examples 41-64 or any combination thereof,where a voltage across terminals of the second energy storage device isless than a no-load voltage level of the first energy storage device.

Example 66. The system of examples 41-65 or any combination thereof,where the second energy storage device is configured to supply power tothe storage controller.

Example 67. The system of examples 41-66 or any combination thereof,where the storage controller is configured to control the low-voltagepower converter to deliver power from the high-voltage energy storagedevice to the storage controller in response to determining the fault onthe low-voltage energy storage device.

Example 68. The system of examples 41-67 or any combination thereof,further including a charging port connected to the bus, where the bus isconfigured to receive power from the charging port when a power sourceand a load are not operating.

Example 69. A system includes a load configured to generate propulsionbased on power received from a bus via a power converter. The systemalso includes a controller configured to determine that a voltagemagnitude on the bus is not less than a threshold level in a firstinstance and cause the power converter to deliver a first magnitude ofpower to the load in response to determining that the voltage magnitudeon the bus is not less than the threshold level in the first instance.The controller is also configured to determine that the voltagemagnitude on the bus is less than the threshold level in a secondinstance and cause the power converter to deliver a second magnitude ofpower to the load in response to determining that the voltage magnitudeon the bus is less than the threshold level in the second instance, thesecond magnitude being less than the first magnitude.

Example 70. The system of examples 41-69 or any combination thereof,where the storage controller is configured to perform each of the methodsteps of examples 8-22 or any combination thereof.

Various examples have been described. Any combination of the describedsystems, operations, or functions is contemplated. These and otherexamples are within the scope of the following claims.

What is claimed is:
 1. An aircraft comprising: a bus; a first powerconverter connected to the bus, wherein the first power convertercomprises a first topology; a second power converter connected to thebus, wherein the second power converter comprises a second topology, andwherein the first topology is different from the second topology; apower source configured to deliver power to the bus via the first powerconverter; an energy storage device configured to receive power from thebus via the second power converter; a source controller configured tocontrol the first power converter; a storage controller configured tocontrol the second power converter; and a system controller configuredto: determine a first set point for the first power converter; transmitan indication of the first set point to the source controller; determinea second set point for the second power converter; and transmit anindication of the second set point to the storage controller; and anelectrical motor configured to propel the aircraft using power sourcedfrom the bus.
 2. The system of claim 1, further comprising: a thirdpower converter; wherein the electrical motor is configured to receivepower from the bus via the third power converter; and a load controllerconfigured to control the third power converter, wherein the systemcontroller is configured to: determine a third set point for the thirdpower converter; and transmit an indication of the third set point tothe load controller.
 3. The system of claim 2, wherein the third powerconverter comprises a third topology, and wherein the second topology isdifferent from the third topology.
 4. The system of claim 2, wherein theload controller is configured to: determine a fault on a communicationline between the load controller and the system controller; and causethe third power converter to operate in an autonomous mode in responseto determining the fault on the communication line between the loadcontroller and the system controller.
 5. The system of claim 2, furthercomprising a motor configured to drive the electric motor based on powerreceived from the third power converter, wherein the third powerconverter comprises an inverter configured to convert direct-currentelectricity on the bus to alternating-current electricity to drive themotor.
 6. The system of claim 1, wherein the power source comprises agenerator that is coaxial with an engine shaft.
 7. The system of claim1, wherein the first power converter comprises a rectifier, and whereinthe second power converter comprises a direct current/direct currentconverter.
 8. The system of claim 1, wherein the storage controller isconfigured to: set a first threshold level or a second threshold levelbased on the indication of the second set point received from the systemcontroller; determine that a voltage magnitude on the bus is less thanthe first threshold level in a first instance; cause the energy storagedevice to deliver power to the bus in response to determining that thevoltage magnitude on the bus is less than the first threshold level;determine that the voltage magnitude on the bus is greater than thesecond threshold level in a second instance, wherein the secondthreshold level is greater than the first threshold level; and cause theenergy storage device to receive power to the bus in response todetermining that the voltage magnitude on the bus is greater than thesecond threshold level.
 9. The system of claim 8, wherein the storagecontroller is configured to cause the energy storage device to refrainfrom discharging or charging in response to determining that the voltagemagnitude on the bus is within a voltage deadband defined between thefirst threshold level and the second threshold level.
 10. The system ofclaim 8, wherein the energy storage device is a first energy storagedevice, the system further comprising: a low-voltage power converterconnected to the first power converter and connected to the first energystorage device; an auxiliary load; and a second energy storage deviceconnected to low-voltage second power converter, wherein the energystorage device is configured to provide power to the auxiliary load. 11.The system of claim 10, wherein the storage controller is configured to:determine a fault on the second energy storage device; and control thelow-voltage power converter to deliver power from the first energystorage device to the auxiliary load in response to determining thefault on the second energy storage device.
 12. A method for controllinga system of an aircraft that includes a bus, the method comprising:determining, by a system controller, a first set point for a first powerconverter connected to the bus, wherein the first power convertercomprises a first topology; transmitting, by the system controller, anindication of the first set point to a source controller, wherein thesource controller is configured to control the first power converter;determining, by the system controller, a second set point for a secondpower converter connected to the bus, wherein the second power convertercomprises a second topology, and wherein the first topology is differentfrom the second topology; transmitting, by the system controller, anindication of the second set point to a storage controller, wherein thestorage controller is configured to control the second power converter;and providing, by a third power converter connected to the bus, power toan electric motor that propels the aircraft.
 13. The method of claim 12,wherein the first power converter comprises a rectifier, and wherein thesecond power converter comprises a direct current/direct currentconverter.
 14. The method of claim 12, further comprising: determining athird set point for the third power converter, wherein the third powerconverter comprises a third topology, wherein the second topology isdifferent from the third topology; and transmitting an indication of thethird set point to a load controller, wherein the load controller isconfigured to control the third power converter.
 15. The method of claim14, wherein the third power converter comprises an inverter configuredto convert direct-current electricity on the bus to alternating-currentelectricity to drive the electric motor.
 16. A device comprising anon-transitory computer-readable medium having executable instructionsstored thereon, configured to be executable by processing circuitry ofan aircraft for causing the processing circuitry to: determine a firstset point for a first power converter connected to a bus of theaircraft, wherein the first power converter comprises a first topology;transmit an indication of the first set point to a source controller,wherein the source controller is configured to control the first powerconverter; determine a second set point for a second power converterconnected to the bus, wherein the second power converter comprises asecond topology, and wherein the first topology is different from thesecond topology; transmit an indication of the second set point to astorage controller, wherein the storage controller is configured tocontrol the second power converter; determine a third set point for athird power converter, wherein the third power converter comprises athird topology, wherein the second topology is different from the thirdtopology; and transmit an indication of the third set point to a loadcontroller, wherein the load controller is configured to control thethird power converter, and wherein the third power converter isconfigured to provide power to an electrical motor configured to propelthe aircraft using power sourced from the bus.
 17. The device of claim16, wherein the first power converter comprises a rectifier, and whereinthe second power converter comprises a direct current/direct currentconverter.